Carrier inductive communication system for vehicles



Sept. 16, 1952 E. w. MARLOWE CARRIER INDUCTIVE COMMUNICATION SYSTEM FOR VEHICLES Filed April 24. 1947 4 Sheets-Sheet 1 mmvrox.

E. W. MARLOWE Sept. 16, 1952 CARRIER INDUCTIVE COMMUNICATION SYSTEM FOR VEHICLES Filed April 24, 1947 4 Sheets-Sheet 2 P 1952 E. w. MARLOWE 2,611,075

CARRIER INDUCTIVE COMMUNICATION SYSTEM FOR VEHICLES Filed April 24, 1947 4 Sheets-Sheet 3 IN VEN TOR.

[Z690 zllazlaz ue. BY 5 Z I Sept. 16, 1952 E. w. MARLOWE 2,611, Q75

CARRIER INDUCTIVE COMMUNICATION SYSTEM FOR VEHICLES Filed April 24, 1947 l 4 Sheets-Sheet 4 IN V EN TOR.

Flberfj Marlowe. BY

Hrs ATIOHVEY Patented Sept. 16, 1952 I CARRIER INDUCTIVE COMMUNICATION SYSTEM FOR VEHICLES Elbert W. Marlowe, Wilkinsburg, Pa., assignor to Westinghouse Air Brake Company, a corporation of Pennsylvania Application April 24, 1947, Serial No. 743,681

My'invention relates to carrier inductive communication system for vehicles, and more particularly to communication systems for railway trains. V

In communication systems for moving vehicles ths transmission must be restricted pretty much to a narrow zone along the trackway to minimize interference with broadcasting and other services, and to this end carrier induction systems have been used. In such carrier induction systems the distance dependable communication can be had between a wayside station and a Vehicle en route is ordinarily much less than the length of "the trackway involved. For example, in carrier telephone systems for railway trains dependable communication between a wayside station and a train is usually confined to a distance of the order of 30 miles, whereas the stretch of track involved may be an entiredivision of 100 to 200 miles. The range of transmission of the communication current is limited in part to the fact that the energy level of the power that may be supplied by a transmitter to a line circuit has been limited by a so-called low power rule.

In a preferred form of inductive carrier communication system, the longitudinal circuit of a line wire, or better, of a pair of line wires, extending parallel to and relatively close to the vehicle trackway is included in a transmitting channel which is inductively associated with vehicle carried circuit elements for transfer of energy between the vehicle apparatus and the wayside. In inductive carrier telephone systems for railway trains, the track rails and the line wires mounted on a pole line along the right-ofway are elements of a transmitting channel due to the distributed impedance of the rails to ground, the distributed capacitance of the line wires to ground, and the distributed inductance between the rails and the line wires. At a wayside station the telephone apparatus is coupled to the transmitting channel by being coupled to the longitudinal circuit of a pair of line wires, or of a single line wire and ground. In view of the socalled low power rule mentioned hereinbefore, the magnitude of the communication energy that may be supplied to'the line wires can be relied upon to provide dependable communication for only a limited distance.

Accordingly, a main object of my invention is the provision of a carrier inductive communication system incorporating noveland improved 6 Claims. (Cl. 246-8) means to extend the range of communication between a wayside station and vehicles en route.

Such limited range of transmission makes it necessary to provide some Another object of my invention is the provision of a carrier inductive communication system incorporating novel means to operate two or more wayside stations spaced apart from a single ofilce location, and an operator at the oflice can use the apparatus of the wayside station in the vicinity of the vehicle with which he wishes to communicate.

Again, a feature of my invention is the provision of improved push-to-talk control of twoway carrier telephone apparatus of a wayside station "from a remote ofiice.

A more specific feature of my invention is the provision of improved means to control a twochannel two-way telephone equipmentof a wayside station of a railway train telephone system from a remote ofiice.

Another feature of my invention is the provision of improved control means wherewith an operator atan ofilce'can selectively communicate with trains in the vicinity of the ofl'ice through apparatus local to the ofiice, or communicate with trains in the vicinity of a remote wayside station through telephone apparatus located at the re mote station.

Other features, objects and advantages of my invention will appear as the specification 'progresses.

The foregoing objects, features and advantages of my invention I attain by the use of a pair of line wires along the stretch of trackway involved, and which line wires can be arranged in both a longitudinal and a'transverse circuit. The line wires in multiple with their distributed capacitance and conductance to ground form a longitudinal circuit, and the two line wires in series form a transverse circuit. These line wires are disposed parallel to and relatively near the vehicle trackway and the longitudinal circuit is inductively associated with vehicle carried circuit elements for the transfer of energy between the vehicle apparatus and the wayside transmitting channel. An ofiice or primary station and one or more remote or secondary stations are located at preselected points along the trackway, the spacing between the stations being such that communication between a station and vehicles can be had for a distance of somewhat more than half the distance between two stations. Generally speaking the distance between the office and a remote station would be of the order of miles, but the invention is not limited to such arrangement and other spacing of the office and remote station can be employed. Each station is provided with a No. 1 and a No. 2 carrier telephone equipment. The No. 1 equipment cooperates with the longitudinal circuit of the line wires for communication with vehicles, and the No. 2 equipment cooperates with the transverse circuit of the line wires for-transmissionof telephone current between the oflice and the remote station.

The No. 1 equipment is of the simplex type including a push-to-talk switch and preferably-it is a two carrier channel arrangement to communicate on either of two carrier frequencies 7S0. as to permit one vehicle breaking in on the conversation between the station and another-vehicle in case of an emergency condition. "It is-apparent, however, that the invention can be used with a single carrier channel system. The No. 2 telephone equipment is of the simplex type using one of two carriers. The oflice or primary. station is attended and the operator controls the No. l equipment-of theoifice by a local switching means and the No. 1- equipment at*the-secondary or remote station through the No. 2 equipments of' the two stations. That is, for telephoning to vehicles within the range of transmission'of the primary station, the operator uses the -No. 1

equipment of the primary station,- and for-telephoning to vehicles within the range of transmission-of the remote station the operator uses the No. 2 equipments for transmitting between the-two stations and the No. 1 equipmentatthe remote station for transmitting-to thevehicles.

*Push-to-talk and control features at the remote station are handled by the operatorat the primary station by control currents transmitted between the-two stations-through the line circuit, .the control currents having characteristics different from thetelephone currents.

I shall describe two forms of apparatus embodying my invention and shall then-point out the novel features thereof in claims.

In the accompanying drawings, Figs. .1a and 11) when taken together with Fig. 1a.- at the-left'are diagrammatic views showingone form of apparatus' embodying my invention when used with a i telephone system for railway trains,- and :wherewith the control currents are of difierent. frequencies. Figs. 2aand Zbwhen taken together with Fig. 2a at the left are diagrammatic views showing a second form of apparatus embodying my. invention. when used with a-railway traintelephone systemand-wherewith polarized line circuits are used for control.

In the different views-like-reference characters areused to designate similar parts.

- It is .to be understood thatthe invention is not limited-to a railway train telephone system, and this one application serves to'illustratethe-many places the apparatus is useful.

Referringto Figs. 1a and 1b, the reference character RT designates a railway trackwhich'may be a continuous stretch or two independent stretches and to aid in the understanding of the: invention I shall considerit is a single stretch of track of a length of the order-of-SOmiles. Two trains indicated conventionally at TR! and TRZ are illustrated as operating over this stretch of ,traclgthe train TRl-loeing considered at some point. within -30'miles' from the left-hand end, and the train TR2 being considered as operating at some point within 30 milesfromtherighthand .end.

,An offic'eOr primary station PS is located near the left-handend. of this stretch-of track and-a secondary or remote station R8 .is. located along *pair-ofline wires extending alongthetrack RT.

These line wires may be carried on the usual pole line along the railway right-of-way. That is, the

jline wires LI and L2 are parallel to and relatively near to the track RT throughout the en- ;tire' stretch of track. The line wires LI and L2 are capable of being used in both a longitudinal .anda transverse circuit. These wires may be wires used in an existing circuit and are used in the inductive carrier telephone system as an additionalservice without interference with their present use. The line wires LI and L2 may be installed for the carrier telephone system alone.

Both the primary station PS and the secondary .stati nRSare provided with apparatus for telephone communication with trains operating on thetrack RT. Thisapparatus-is of the inductive carrier type and each apparatus includes a No. 1 and a No. 2 equipment or assembly, together-with control and switching means-and suitable sources of-power.

The-No. 1 assembly is indicated as a' whole by a dotand-dash rectangle 'ITC at each station and each assembly is capable of, communication with trains within a given range of the respective station. Each ITO assembly is of the two channeltype capable of communicating on either'a first or a second carrier frequency,1-such' asa carrier frequency of 88 kc. and 144'kC.,-I8SDC- tively; although other carrier frequencies can be used. --As here, shown, .each lTc-assem'blyineludes two independentreceivers and. a'transmitter. One receiver designated-R88 is forusewith the firstcarrierchannel of 88 kc; and the other receiver designated R144 is forusc withthesecondcarrier channel of 1441 kc. The transmitter designated TN is capable'of being conditioned to supply current ofeither the first or second carrier frequency. These devices -may take: different known .forms; and are shown conventionally for the sake of, simplicity. These devicesmay, for example, :be similar to those disclosed in an application for Letters Patent of the United States. Serial 'No. 575,311, filed January 30, 1945, by Paul N. 'Bossart, for Railway Train Communication Systems, now Patent No. 2,484,680, issued October 11, 1949. I It isv suflicient for the present application to point outthat the receivers R88.and

RIM have their input coupled in multiple to the longitudinal circuit of the'linewires. LI .and L2 through transformers I0 and I |,respectively, and the output of the transmitterTN, coupled to thelongitudinal circuit through-a transformer .12. The two receivers R88 andRlMare normally conditioned for receptionpancl the transmitter TN is-normally inactiveand energized and made active only=during the sending from the respective station.

. As here shown, .the power-source at each station includes azmotor generator, a motor Ml of which is powered from alowvoltagedirect current.-source, such as 32 volt batteryhaving :terminals B and N, and a generator G of which supplies a relatively 'high' voltage suitable-Tor energizingthe. anode circuitsof the various electron tubes of the'different devices as will appear from timeto time. The terminals of the. generator-G are-indicated at BA and'NA, thenegatiye terminal NA- and the positive terminalsB of. :the

low voltage source being preferably connected to ground. In several instances, relay contacts are shown in the drawings remote from the'relay winding for the sake of simplicity. In each case the contact is given the reference character of the respective relay plus a distinctive numeral.

To normally condition the receivers for reception, the anode circuits of the tubes of the receivers are normally connected to the generator G. The anode circuits for the receiver R88 include back contact 14 of a power relay IP, to

be referred to later, and the anode circuitsfor the receiver R144 include back contact l5 of a power relay 2P, also to be referred to later. The transmitter TN is energized from generator'G when relay IP is picked up closing front contact l6 and also when relay 2P is picked up closing front contact H. The transmitter TN is conditioned to supply the carrier of 88 kc. when a relay L3, to be referred to later, is released to close back contact l8 and a capacitor I9 is interposed in the associated oscillator circuit, but when relay L3 is picked up closing front contact 20, a capacitor 2| is interposed in the oscillator circuit and the transmitter is conditioned to supply the carrier current of 144 kc.

Each ITC assembly also includes a calling oscillator CO adaptable of generating an individual tone frequency for each of the carrier frequency channels. The oscillator CO may be a standard form oscillator and it is shown conventionally. Itis normally active and it is conditioned to supply the tone frequency for the first or 88 kc. channel when a relay Ll is picked up closing front contact 22 to include a capacitor 23 in the oscillating circuit and it is conditioned to supply a tone frequency for the second or 144 kc. channel when relays LI and L2 are both picked up closing contacts 22 and 24, respectively, to interpose capacitors 23 and 25 inthe oscillating circuit. The output of the calling oscillator 00 is coupled to the associated transmitter TN to modulate the carrier frequencyby the respective tone frequency, a transformers and a front contact l3 of relay' Ll being included in a coupling circuit to be more completely explained hereinafter.

The No. 2 telephone equipment at each station comprises two carrier telephone units designated CTI and GT2, respectively. These units are alike except for the carrier frequency used and a description of one is sufficient for an understanding of all. To aid in the understanding of the invention, I shall assume that the unit CTI uses.

a; carrier frequency of 39 kc. and the unit 0T2 uses a carrier frequency of 33 kc., although other frequencies can be used. Looking at the unit CTI at the station PS, it includes a transmitter T39, a receiver R39 and a switching relay D1. The transmitter T39 and receiver R33 are shown in block form because they can be of standard arrangement. Theseunits may be of a structure similar to that disclosed in an application for Letters Patent of the United States, Serial No. 655,071, filed March 18, 1946, by Ralph K. Crooks, for Communication Apparatus, now Patent No. 2,432,560, issued December 16, 1947. It is suffitransverse circuit of the line wires LI and L2, the arrangement being such that when relay Dl 'is picked up closing front contacts '26. and- 21,- the inputside of receiver R39 is connected i across the line wires LI and L2 through blocking capacitors 2B and 29, and when relay DI is released opening front contacts 26 and 2Tand'closing back contacts 30 and 3| the receiver R39 is disconnected from the line circuit and the output of the transmitter T39 is connected thereto."-= The output of the receiver R39 is also controlled 'at front contact 32 of-relay DI, as will be explained shortly. The relay Dl at station PS isnormally energized by current supplied from the-genera responding units at the primary stationP-S.

That is, the two CTI units cooperate for transmitting a carrier telephone current of the carrier of 39 kc. between the two stations and the two GT2 units cooperate to transmit carrier telephone current of the carrier 33'kc. between the two stations. It is to be pointed out that the'two control relays DI and D2 at theremote station RS are normally shunted and released so that the associated transmitters are connected to the transverse line circuit. f j

The apparatus at the remote st'ationfRS "is governed by the operator at the primary station PS by means of control currents of different frequencies transmitted between the two stations by the transverse line circuit. At the primary station PS a control unit CU is provided with two oscillators indicated conventionally at 34 and 35, the oscillator 34 supplying a first control current of a frequency of say fl and the oscil1ator35 supplying a second control current of a frequency of say 12. These frequencies fl and f2 are preselected and are made different from any of the carrier frequencies used in the telephone com-- munication system. The arrangement is such that when a control relay GI is energized closing front contact 36, the oscillator 34 is powered from generator G and control current of the frequency fl is applied to the line circuit and when a control relay G2 is energized closing front contact 31, the oscillator 35 ispowered and control'current of the frequency f2 is supplied to the line circuit. At the remote station RS two control frequency selectors PSI and F82 are connected in multiple across the line wires. These devices FSl and PS2 are shown in block form since they Kl in response 'tocontrol currentfof'the frecient for this application to point out that the transmitter T39 includes an oscillator of a carrier frequency and means for modulating the carrier by. voice frequencies. Also, the receiver B39 includes a demodulator of such carrier telephone current.

The relay Di governs the connections of the transmitter T39 and the receiver R39 to the quency fl and the selector FS2 fincludin'ga filter and a rectifier to energize a relay'KZ in response to'control current of the frequency 12. I

' The relays Kl and K2 are preferably of the bias polar type, the arrangement being such'th'a't their armatures are biased to the right-hand position, that is, the position shownin'the draw ing, and their armatures are operated'tofthe left-hand position when the relay is energized by the current supplied through the respective selector. A stick polar relay SP and a'neutral relay NP are associated with the relays'Kl and .K'Ztto; govern. the. operation: of the-remote. stationapparatus; as will be explained when the .the operation of. the apparatus at the'station PS :andalso at the remote station RS through the :medium of a transfer switch TS, a channel selector-switch- SS and a calling switch CS. These switches are shown as of the three-position multiple contact type. The transfer switch TS, for example, is operated to a center or. stand-by position.- a left-hand .or remote control position and a right-hand or localcontrol position by movement of-its handle 38 to a center, a'lefthand, and agright-hand position, respectively.

The construction is such that when "the handle 381s moved to the left, a contact actuating member 115 of suitable. insulating material is moved to the'left and a contact actuating member I l6 also of insulating material remains in the position it is shown in the drawing, but when the handle 38 is moved to the right, member ll6=is moved-to the right and the member H5 is left in the position shown.

Similarly, the channel selector switch-SSis operated to a stand-by position,.a high carrier channel position and a low carrier channel position by movementof its handle 39 to av center,

aleft-hand, and a right-hand position, respectively. The construction is such that the handle IQ-when moved. to the left .actuatesi a contact actuating 'member. -I ;l l of. insulating material to .the left, leavingan-insulation contact actuating member. :H 8 stationary and when handle-39 is movedto theright, the-member 'll8rismoved .tothe right but the member -l H is. left stationary.

-..An;inactive condition of the. calling switch. CS is eifected when its handle ;4B;-is set at at center position,:a highchannel 'calling condition is affected when the handle 40 is movedto the-left, and alow channel-calling condition isefiected when the handle is moved'to the right. :The construction is --such that handle 40- whenmoved to the 'left first moves a-.contactactuatingnnember M9 and then: a contact actuatingxmember .120, leaving. two; other contact actuating: mem- 'bers -.-l.2l and J22 stationary. A movement;.:of .the. handle 40 to the; right firstz causesimovd merit-of contact actuatingmember 12 I and then .movement. of member. I .22,- cleaving :members; 11 9 and 1-12 0- stationary.

..At-the, primary station *PS :the circuit wires between the several devices arexshownrrunjn cablesin order to simplify :the drawing. ';;Each circuit .wire is identified by. a numeral placed ateach end ofthe wire.

. Each train TRI and TRZ is provided with-twoway communication apparatus adapted to cooperate with the ITC- assemblies of .the wayside stations through .the trackway transmitting channel which includes the longitudinal circuit ofthe linewires. This transmitting channel is explained-more. fully. in Letters -Patent.=.of the United states, -No. 2,064,642,-- granted December l5,e1936;to Paul :NrBossart. for RailwayTrain Communication Systems. The apparatus/f eachtrainpreferably. includes a transmitter TN and-two receivers'R88 and Rl44. similar/to the corresponding devices at the wayside stations. carried transmitterTNis coupledto and the line Wires and communication current flows in the longitudinal circuit of the line wires. The train carried receivers R88 and RI are connected to pick-up coils PCI and P02, respectively, and each of which coils is mounted. for inductive relation with the trackway transmitting channel. Thus, carrier communication current supplied to the transmitting channel .to flow therein causes a transfer of energy .to the train carried receivers.

In describing the operation of the apparatus of Figs. 1a and 1b, I shall first consider the stand-by condition, thatis, the condition-during non-communication and in which condition the apparatus is illustrated in the drawings.v In thisstand-by condition, the two receiversR88 and R144 of the ITC assembly at each station are energized and the transmitter TN is inactive.

Looking at the primary station PS, the receivers R88 and Rl44 have their outputs normally connected in multiple to a loud-speaker LS. The output circuit of the receiver R88 can be traced from the upper right-hand terminal of the receiver through wire 4| in cable CAI, normally closed contact 42 of transfer switch TS, a test switch 43, wire 44 in cable CA2 to a terminal of switch SS, wire 45 in cable CA3, loud-speaker LS and through the ground path back to the other sideof the output of receiver R88. The output side of receiver Rl44 extends through wire 46 in cable CAI, contact 41 of switch TS, test switch 43 and thence to the loud-speaker, as traced for the receiver R88, and back to receiver Rl44 through the ground path.

Both-receivers R39 and. R33 of the carrier telephone units CTI and GT2 at station PS are energized and their outputs connected to the loud-speaker LS in multiple with the receivers R88 and RIM. The output of the receiver-R39 includes wire 48 in cable CA4, normally closed contact of switch TS, wire 44 in cable CA2, wire 45 in cable CA3, loud-speaker LS, ground and front contact 32 of relay DI. Similarly, the output of receiver R33 extends through wire 50 in cable CA4, a normally closed contact 5| of switch TS, and thence to the loud-speaker as previously traced and through the ground and front contact 52 of relay D2. It follows that during the stand-by condition a calling current or a telephone current received at the station PS from the longitudinal line circuit is demodulated at receiver R88 or R|44 as the case may be and the calling tone or message is-sounded at the loud-speaker. Also, any calling current or telephone current of the carrier 39 kc. or 335110. received at station PS from the transverse line circuit is demodulated at receiver R39 or R33 as the case may be, and the corresponding calling tone or message sounded at the loud-speaker.

Under the stand-by condition of the apparatus at the remote station RS, the relay DI of .the unitCTl .is shunted by a path including wire 9 53, low impedance input of transmitter T39, wire 54, low impedance output of receiver RI44, wire 55, back contact 56 of relay NP and ground; and the relay D2 of the unit CTZ is shunted by a similar path including wire 51, low impedance input of transmitter T33, wire 58, low impedance output of receiver R88, wire 59, back contact 60 of relay NP and ground. With relays DI and D2 shunted, the outputs of the transmitters T39 and T33 are coupled to the transverse line circuit. Thus a calling current of the low or 88 kc. carrier channel received from the longitudinal circuit at station RS is demodulated at receiver R88 and the tone frequency is applied to the transmitter T33 to modulate the 33 kc. current and the output of transmitter T33 is applied to the transverse line circuit for transmission to the primary station PS where the current is received at the receiver R33 of the unit CT2 and demodulated and the tone frequency applied to the loud-speaker LS. In like manner a calling current of the high or 144 kc. channel received from the, longitudinal circuit at the remote station RS is demodulated at receiver RI44 and the tone frequency applied to the transmitter T39 to modulate the 39 kc. carrier and this modulated carrier current is applied to the transverse line circuit for transmission to the primary station PS where it is demodulated at receiver R39 and the calling tone applied to the loud-speaker.

To sum up, the stand-by condition of-the apparatus permits either train TRI or TRZ to call the operator at the primary station PS on either of the carrier channels. The calling current from train TRI which is operating within the range of station PS is received through the ITC assembly of station PS and the calling current from train TR2 which is operating within the range of the remote station BS is received at station RS through the ITC assembly and transmitted from the remote station RS to the primary station through either the CTI or the C'I2 unit. In the event a call is received at station PS the operator can determine if the call comes from train TRI or train TRZ by operating the test switch 43. If the call continues with switch 43 open, the operator knows the call is from the remote station RS, and if it ceases with switch 43 open, the call is coming from the train TRL j I shall next assume that the operator at the station PS desires to communicate with the train TRI through the low 88 kc. carrier channel. To do this, the operator sets the switch TS to its right-hand or local position, and the selector switch SS to its right-hand or'low carrier position. The operator then would operate the calling switch CS to the right to send the calling tone of the low carrier channel. A circuit for relay IP is now formed from terminal B through contact I3 of switch TS, winding of relay IP, wire BI in cable CA and contact 62 of switch CS to terminal N, and relay IP is energized to open back contact I4 and close front contact It so that the receiver R88 is deenergized and the transmitter TN is energized. Relay LI is also energized by a circuit including terminal B, winding of the relay, wire 63 in cable CA5, contact 64 of switch CS and terminal N. With relay LI picked up closing front contacts 22 and I3, the calling oscillator CO is conditioned to supply the tone frequency for the 88 kc. channel and the output of the calling oscillator is connected to the transmitter TN to modulate the 88 kc. carrier by the tone frequency. The connectionfor the calling oscillator to the transmitter includes wire 65 in cable CAI, contact 66 of switch TS, wire 61 in cable CAI and the input of the transmitter. This calling current thus applied to the longitudinal line circuit is available to influence the receiver R88 of the train TRI.

Subsequent to the sending of the calling current the switch CS is restored to its normal condition so that relays IP and LI are deenergized and the ITC assembly is restored to its normal receiving condition. With the switches TS and SS set at their right-hand positions, the output of the receiver R88 is switched from the loudspeaker LS to the earphones of the hand set HS, the connection being completedthrough wire. M in cable CAI, contact 68 of switch TS, wire 69 in cable CA2, contact III of switch SS and wire II in cable CA3 to the earphones, the other side of the circuit being. completed through ground. Thus a reply from train TRI is sounded in the earphones. The operator can receive the reply from train TRI at the loudspeaker by setting switch SS at its stand-by position to complete the normal connection of receiver R88 to the loudspeaker.

To send from station PS during the two-way conversation with train TRI, the operator uses a press-to-talk switch I2 of the hand set. With switch I2 closed, the relay IP is energized by current flowing from terminal B through contact I3 'of switch TS, winding of relay IP, wire BI in cable CA5,'wire 14 in cable CA6, contact I5 of switch SS, wire 16 in cable CA3, and press-totalkswitch 12 to terminal N. With relay IP pickedup to 'deenergizereceiver R88 and energize transmitter TN, voice frequencies created by talking into a microphone M of the hand set is applied to the transmitter TN for modulating thecarrier current, a microphone circuit being traced from terminal B through ground to the input of transmitter-TN, wire' 61 in cable CAI, contact BI of switch TS, wire in cable CA2, contact I9 of switch SS, wire 18 in cable" CA3, microphone M and front contact -I'I'of relay IP to terminal N. r

It follows that by using thepress-to-talk switch I2, the operator can carry on a two-way conversationwith the train TRI by use of the 88 kc. channel. During this conversation the receivers RI44 and R39 and R33 are connected to the loud-speaker ready to receive a call, the circuit connections for receivers R39 and R33 being the same as in the stand-by condition but the connection for the receiver RI44 being now completed through wire 46 in cable CAI, contact 82 ofswitch'Ts wire 83 in cable CA2, contact 84 of switch SS and wire 45 in cable CA3 to the loudspeaker. 1

. Inthe event the operator wishes to communicate with train TRI using the 144 kc; channel, the switch TS is set at the local or right-hand position and switch SS is set at the left-hand" or high channel position. The calling switch CS is moved to the left for sending a call. Relay 2? is now energized through a connection including terminal 'B, contact 13 of switch TS, windingof relay. 2P, wire85 in cable CA5, contact-86 of switch CS and terminal N. -Relay 2P- on picking up 'to open back contact I5 and closefront contact II dee'nergizes the receiver RI44 and energizes the transmitter TN. The relays L3, L2, and-LI are-now. all energized, the relay L3being rovided with acircuit extending from terminal B through Winding ofthe relay, Wire 81 in cable CA and contact 88 of switch CS'to terminal'N. Relay L2 is energized byJcuIrent flowing from terminal B through winding of the relay, wire 89 in cable CA5, andcontact 90 "of switch CSto terminal iN. The circuit for relay'LI includes terminal B, winding of the relay, front-contact SI of relay L2 and the circuit previously traced for relay L2. Withrelay L3 picked up closing front contact, the transmitter TN is condition'ed'to supply the 144 kc. carrier, and'with relays LI and L2 picked up the calling oscillator CO is condi-' tioned to supplythe tone frequency for'the144 kc. carrier'-and'the output-o1 the" oscillator CO is coupled to the input of the transmitter so that the calling:current is'appli'ed' to the longitudinal line' circuit and is available to influence'thereceiverR'I 44 on the: traim After sending this calling current, the switch CS is restored to'its center position and the operator can carry .on a two-waymonversation byusing. the press to talk switch 12; When'the switch "12 is closed" to 'send from the primary stationpth'erelay 2P-is energized to cut out'the receiver-Rl'44'jand to cut int'he transmitter TN," the circuit for relay 2P being completed through contact I3 of switch TS, winding of relay 2P, wire 85- in cable CA5, wire 92 in cable CAByconta'ct 93 of switch SS; Wire'IS in'cable' CA3 and switch I2 to terminal N. The relay L3 is also provided with a circuit to'condition-the transmitter for supplying 'the144' kc-.-carrien thecircuit for relay- L3 including terminal B, winding ofrelayii-L3, wire 81 in cable CA5,- wire 94 in cable CA6, con tact 95 of switch SS, wire I6 in cable CA3, switch 12' andtermina'l N;' The earphones of the hand set are now connected to the output-of "the receiver R I44 to receive the conversation, the connection being completed'through wire 46 in cableCAI, contact82-of switch TS; wire in cable'CA2, contact SIB-"of switch SS, wireII- in cable CA3 and ground.-- The microphone isnow connected tothe transmitter TN through input of trans m-itterTN, wire 61- in-ca-bleCAI, contact I of switch TS, wire I in cable CA2, contact I- of switchSS, wire- 18 incable CA3, microphone M, front contact I 68 of relay 2P, and terminalN. During the conversation,- the receivers R88, R39 and R33 are connected to the-loud-speakerto receive a call, theconnections for the-receivers R39 and R33 being the-same asunder the standby condition, butthe connection'for receiver R88 including r wire 4I -in-cable-CAI; contact B8 01' switch TS, wire 89 in cable CA2-,- contact -87 'of switch SS and wire incable CA3.-

It follows from the foregoing description that the operator can carry on a two-way conversation with train TRl on either carrier-channel through the ITC-assembly of the primary station PSand during a conversation on eitherxoneor the other of the carrier-channels',-the receiver ofthe other channel and-the receivers of the units CTI and GT2 are connected to the-loud-speaker so that a call can be'recei'ved.

I shall next consider theoperationwhen the operator at station PS wishes to talk-to the train TR2 in the vicinity of the remote station RSrthe operator carrying on the conversation: by theapparatus at the remote "stations Under these circumstances, the switch TS is set at its' left hand or remote position and the channel 'selection switch CSis set at the right-hand position if the operator desiresto carry'on conversation on the '88 'kc. channel. Also, when'the operator uses the -88 'kc. channel for communication with 12 a train, then the 33 kc. channel is used for transmission between the two stations.

To send a call on the 88 kc. channel the operator moves the calling switch CS to the right. The first thing to occur under this condition is that the two control relays GI and G2 of the control unit CU are energized sequentially in the order named due to the construction of the contacts of the calling switch CS closing the circuit for relay GI first. The circuit for relay GI can be traced from terminal B through ground, winding of relay GI, wire 98 in cable CA4, contact 99 of switch TS, wire I00 in cable CA2, wire IOI in cable CAB and contact I02 of switch CS to terminal N. The circuit for the relay G2 includes ground, winding of the relay, wire I03 in cable CA4, contact I04 of switch TS, wire I05 in cable CA2, wire I06 in cable CA6, the later closed con-. tact I01 of switch CS and terminal N. With'relays GI and G2 energized sequentially the connections for the oscillators 34- and 35 are completed sequentially and their currents are transmitted to the remote station to energize relays KI and K2 sequentially. The closing of contact 1 I08 of relay KI completes a simple circuit for the lower winding of relay SP and its polar armature is operated to the left-hand position, if it is not already in this position. The subsequent energization of the top winding of relay SP when contact I09 of relay K2 is closed does not change the position of the polar armature of relay SP due to its polar stick characteristic. Both windings of relay NP are energized with the operation of relays KI and K2 and relay NP is picked up so that current flow from terminal B through the control relay I P of the station RS, the connection being completed at contact III! of relay SP and front contact III of relay NP. With relay IP at station RS picked up to open its back contact I4 and close its front contact I6, the receiver R88 is-deenergized and the transmitter TN is energized. Current also flows from terminal B through winding of relay LI at station RS, contact II2 of relay SP, contact II3 of relay K2 and contact II4 of relay KI to terminal N, and relay LI is picked up to close its contacts I3 and 22 so that the calling oscillator CO at the station RS is conditioned to supply the tone frequency for the 88 kc. channel and there is completed'aconnection betweenthe output of the calling oscillator and the input of the transmitter TN for modulating the 88 kc. carrier by the low calling tone with'the result that this calling current is applied to the longitudinal line circuit at station RS-and is available to influence the receivenmfi of the train TR2.

Subsequent to the sending of this calling-current'theoperator restores the switch CS :to its mid "position so "that-the relays GI and G2 are deenergized and the iappara'tus of the two stations is'made ready'to transmit a reply from train'TR2; Afreply from tr'ain TRZ wilLbe de-' modulated at receiv'er'fifia-of the station RS and the voice frequen'cies applied to the transmitter T33 and the corresponding carrier telephone current applied to the transverse line circuit for transmission to the-primary station PS. At sta' tion; PS this current is demodulatedat receiver R33 and applied to the-earphonesof the hand set, the connection of" the earphones including wire in cable CA4, contact" I23 of switch'TS, wire I'M in cable CA2, contact -'I25'-'ofswitc'h'SS, wire II in cable CA3,-earphones'andground connectionr- It is to bepointed-out that the operatorat station PS can receive-the reply from "train 13. TR2 at the loud-speaker by setting switch SS at its stand-by position, the receiver R33 being then connected to the loud-speaker through contact I of switch SS in place of being connected to relay KI at station RS. The lower windings of polar stick relay SP and neutral relay NP are energized so that relay SPWis held at its left-hand position and relay NP is picked up. Under these conditions the relay IP at station RS is energized to switch the receiver R38 and the transmitter TN at that station. Also, the picking up ofrelay NP opening back contacts 56 and removes the shunt of relays DI and D2 and they pick up to switch the units CTI and GT2. At station PS a microphone circuit is formed from ground through front contact I28 of relay GI, microphone M, wire I8 in cable CA3, contact I9 of switch SS, wire 80 in cable CA2, contact [21 of switch TS, wire I26 in cable CA4, input side of the transmitter T33 and resistor I29 to terminal BA. This path through the microphone also serves to shunt the relay D2 at station P3 with the result the output of the associated transmitter T33 is connected across the transverse line circuit so that the voice frequencies created in the microphone of the hand set serve to modulate the 33 kc. carrier of the transmitter T33 and the resultant carrier telephone current is transmitted to the remote station where it is received by the receiver R33 of the unit GT2 at that station and demodulated, since the input of receiver R33 at station RS is now connected to the transverse line circuit. The voice frequencies in the output of the receiver R33 at station RS are applied to the input of the transmitter TN since this connection is closed at front contact 52 of relay D2 at station RS and the corresponding modulated carrier is applied to the longitudinal line circuit and is available for influencing the train carried receiver R88. Thus by use of the press-to-talk switch I2 a corresponding press-totalk control is effected at the remotestation RS and the operator can carry on a two-way conversation with train TR2 through the ITC assembly of the remote station.

During this time the loud-speaker at the primary station is' connected to the outputs of the receivers R88, RI44, and R39, the connection for,

the receivers R88 and RI44 being the same as under the stand-by condition, and the connection for the receiver R39 including wire 48 in cable CA4, contact I30 of switch TS, wire I3I in cable CA2, contact I32 of switch SS, wire in cable CA3, loud-speaker, ground and front contact 32 of relay DI.

Should the operator wish to use the 144 kc. channel for communicatingwiththe train TR2, the operation of the apparatus is similar to that just described for carrying on a conversation byl se of the 88 kc. channel. This time the operator moves the switch SS to the left-hand and operates switch CS to the left energizing the two control relays G2 and GI sequentially in the order named, the connection for relay G2 being completed at contact I33 of switch CS and the con-.- nection for the relay GI being completed at the later operated contact I34 of switch CS.

At theremote station RS the reception firstof the control current of frequency f2 energizes the relay K2 and in turn energizes the top winding of the polar stick relay SP to operate its polar contact to the right hand before current is received of. the frequency II to operate relay KI andenergize the lower winding of relay SP. This means that relay SP is held at the right-hand po-,

sition,v and the neutral relay NP is picked up. The relays 21? and L3 of station RS receive current through the right-hand contact I35 of relay SP and front contact III of relay NP. Also, the two relays L2 and LI at station RS are provided with a circuit completed at contacts .4. I I3 and I36 of relays KI, K2 and SP, respectively.

This control of the relays 2P, L3, ,L2, and LI at. station RS deenergizes the receiver RIM and,

energisedthe tansmitter TN, the transmitter TN being conditioned to supply the 144 kc. carrier. Also, the calling oscillator CO at station RS is conditioned to supply the tone frequency for the 144 kc.'carrier for modulating the output of the transmitter TN and consequently this calling current of the high carrier channel is applied to the longitudinal circuit andis available for actu-.

ating the receiver RI44 of train TR2.

Two-way conversation is subsequently carried on by the operator restoring the calling switch CS to its mid position and using his push-to-talk switch I2. A reply from train TR2 in response to the calling current is received at the receiver RI44 of, station RS and the voice frequencies are applied to. transmitter T39 so that a carrier telephone current of the 39 kc. carrier is transmitted to the primary station over the transverse line circuitand is received at receiver R39 at station PS and the message sounded in the earphone'of the hand set HS since the output of the receiver R39 is now connected to the earphone through wire 48 in cable CA4, contact I30 of switch TS, wire I3I in cable CA2, contact. I3I of switch SS and wire II in cable CA3 to the earphone. Again, it is to be pointed out that the operator can receive the reply from train TR2 at the loudthe control relay G2 is picked up the control cur rent of frequency i2 is sent to the remote station to operate relay K2 and subsequently retain relay SP at its right-hand position and energize relay NP. This means that the receiver RI44 at the remote station is deenergized and the transmitter TN is energized and conditioned to transmit on the 144 kc. carrier. Also, relay DI of unit CTI is picked up and that unit is conditioned to receive current from the primary station. The

microphone circuit is now completed from ground through front contact I39 of relay G2, micro-' phone, wire I8 in cable CA3, contact I40 of switch SS, wire MI in cable CA2. contact I42 of switch TS, wire I43 in cable CA4, input side of transmitter T39, and resistor 33 to terminal BA. This path also shunts the relay DI and the relay DI is released to connect the output of the transmitter" Tu to the transverseline circuit so 'that voice frequencies created in the microphone and applied to the transmitter T39- cause telephone cur-- rent:of-- 39 kC.-08.lll61 to be'transmitted to I the remoteastation; Atstation RS this current is re-- ce'ived-et receiver=R39 and demodulatedand the voice frequencies are applied to-the input of transmitter TN with the: result: that a carrier thez144: kci carrien channel through' the' remote station apparatus.

. Referringto Figsxza and the apparatus isthe same-- as that ofFi'gsr 1a and .121, except for the =use=of a' polarized linecircuit to control the remoteistation in place of a frequency control and to use the callin'guoscillator at the primarysta' tionifor providing a call through the remote stationrin place: .of a separateicalling oscillator at thetremote station";

Itusf'believedxthatthe apparatus of Figs. Zaand 2b canbestbe understood from:adescription of itsltoperation taken in connection with r the descriptionnfrthe apparatus-ofFigs. 1a" and 1b.

. Under-the stand-by condition of the apparatus ofoFigsz: 2a. and 2b, the receivers R88 and RI44 ofsth'e ITC assembly and the receivers R33- and Rae-of? the CT2 and. CTI. unitsat the-primarystatiomcPSi are .connectedtothe loud-speaker in multiple. readytto receive a call from the trains. operatingain. the stretch of. track .RTV At the: remote-station .RS,.the receivers R88 and RI44 of thelTC assembly; are conditioned" for reception and the: transmitters T3 9: and T33 of: the CT I and GT2- :units are :conditioned to transmit. to the primary "station: any 1 call. received 'through the: ITC assembly.

: In the case. the operator desiresit'o communicate; with train 'IRI within the range of transmission of'lthe primarystation PS, he setsthe switchTS atithe'local orright-hand position andthe' switch SS at the carrier channel position corresponding to'the carrier channel he is going to use'and'then operates the calling switch CSaccording to the carrier channel to be used to send a call; Theoperation of the-equipment for communication with the train TRL is the same as described for the operation of the apparatus Ot'Figs; 1a and lb andzther description of'this-lportion. of the op:- eration of; the apparatus of Figs; 2a: and- '2b need not berepeated. I

I shall' next'takerup the operation "of the 'apparatus whemtheoperator wishes tc. comrnunicate-withi a train; such asrtrairr TR2', within the range of-transmission of the remote stationrRSy and I- sh-all 1 assume first that the-operator is Under these circumstances, the-operator.sets-the switch TS at: its left-hand 01 remoteposition; and. switch SS" atithe right-hand-or low-channelpositionr: To send a call, the calling switch CS-is moved' to-thv right.- Acontrolrelay G3--is energized-bythisusing-the 88 -kc'.; carrier channel;

operation or. the calling switch CS; current-flown 16 ing from terminal B through contact I45 01- switch ETS; wire I 44 in cable CA4, Windingof 112-- lay-G3, wire I 46 in cable I CA3 contact I 52 -ofswitch SS ,'"wire I59 in 'cabIe -CAS, and contact lfidofiswitch CS'tO terminaI-N. With relay G3 picked up, a -line= battery I53 -has--oneterminal connected to" the :linewires LI and L2 -in multiple th'rough front' contact" -I 55 ofrelay- G3 and a repeateror simplexcoil-I56,- andits other term-inal connected to ground through front-com tact I54 of relay (33. At -station RS this-control current 'from: battery I 53 I is supplied to relays K3 and- K4 inseries through a simplex-coil-I51 and the current is of a polarity thatthe relay-K3 isoperate'd :to the left-hand position, but; relay K4 is energized wit-h its polar-armature held at" the biased-:iig'ht-hand position; the relays-K3 and K4 l-being bias polar. relays;

With :the control relay K3 reversed; the power control: relay IP at station RS is energized-by an obviousl circuit including .contact' I 58 of relay K3. and relay 'IP :on picking up serves to switch the receiver R88 and transmitter TN at-station RS. Also,the=openingoficontactzlfifl of relay Ka serves to-remove a shunt path of. relay D2 of the unit CTZ and relaytDZ is-picked up-and the receiver: R33 of that: unit iSzCOIlITBCtBd to I the transverse line: circuit to receive carrier telephone current from'czthecprimary station. At the primarylstation PS themoving of. the switch CS tothe right 'servesto-complete' at its contact 64 the circuit forrelay Ll,iand' relay LI on picking up conditions the calling osciliator C0 to supply the calling ;tone':for the: 88Jkc.- channel." The output. ofthe oscillator CO is now connected: to

the transmitter T33 atthe' primary station by a I connection 'completed through wire in cable CAi, contact-I48 of's'witch:TS;wire I49 ineable' CA2 to a tap atthe right-hand end of switch SS,

contact I5I of switch'SS;-wire 8D in cable CA2, contact 1210f switch TS, wire 126' in cable CA4,

input-side'of transmitter T33 and'terminal BA.

This-path serves: also to shunt the relaylDZ of unit C'IZ of-station'PSand relay D2'is released to connect the: output of transmitter1'133 tothe" transverselinecircuit so that'the'33 'kc. carrier is modulated by the tone: frequencies supplied from theoscillator CO- and the calling current'is transmitted to sta-tio'n- RS' Where the current is received-and demodulated at the-receiver R33 and the tone frequencies are applied to the input of-the transmitter TN of station RS to modulate the 88 kc. carrien: :Thisresults' in calling. current oi :the. low channel frequency being supplied to-the-longitudinal circuit-atstation- RSand made available to actuatethe receiver R8Ir of the train TRZ.

Subsequent -to--t-he sendingof this calling current the operator would movethe'switch CS to .itsmid-positionw Thiscau'ses the control relay 5 G3 to be deenergized andin -turn the polar relay I K3 of-theremote station isreturned to its biase'd- I position: and -'the-.appar'atus at: the stations is ready to receive from the train; A reply from thevtrain 'I'RZ- is received at the-receiver R88 at station RS and demodulated and-"the :voicefrequencies applied to thetransmitteri T33 and the' corresponding carrier-telephone current suppliedto the"transverse circuit for transmission to the primary station PS whereit i's received at' the-receiver R33and-demodulated and-the voice frequency sounded at the "earphone ofthehand set-"whichdsnowmonnected to the outp'ut' of the receiver Rain-the rconne'ction beingthe-same as described injFignlas 17 The operator uses his'push-to talk switch I2 to reply to the train TR2. The switch 12 controls the relay G3, the switch I2 is closed, through a connection from terminal B, contacti45 of switch TS, wire I44 in cable CA4, relay G3, wire I48 in cable CA3, contact I52 of switch SS, wire I6 in cable CA3. and switch 12 to terminal N. With relay G3 energized, then the control current from battery I53 is applied to the line circuitfor reversing the relay K3 at the remote station to switch the apparatus at that station. The microphone M is now connected to the input of the transmitter T33 the same as in Fig. 1a except to include front contact I'll of relay G3, and relay D2 of unit T2 is shunted to connect the output of transmitter T33to the transverse line circuit and the voice frequencies created in the microphone serve to modulate'the 33 kc. carrier and the corresponding carrier telephone current is transmitted to the remote station RS. At the remote station the reversal of the polar relay K3 causes the relay IP to be energized to switch the receiver R88- and transmitter TN, and also to switch the unit CTZ from the transmitter T33 to the receiver R33 so that the carrier telephone current now transmitted from the primary station PS is demodulated at receiver R33 and the voice frequencies are applied to the transmitter TN to modulate the 88 kc. carrier and the corresponding carrier telephone current is applied to the longitudinal circuit for transmission to the train TR2.

To use the 144 kc. carrier channel for communication with train TR2. the operator would set the switch TS for remote control and switch SS at the left for the high channel. Then to send acalling current the calling switch CS is moved to the left. This condition of the control switches serves to energize a relay G4 at the station PS, current being supplied from terminal B through contact I45 of switch TS, wire I44 in cable CA4, winding of relay G4, wire I4! in, cable CA3, contact I6I of switch SS, wire I52 in cable CA6 and contact I63 of switch CS to terminal N. With relay G4 energized the control battery I53 is connected to the line circuit at a polarity the reverse of that when relay G3 was selected and the control current serves to energize the relays K3 and K4 at the remote station at a polarity such that relay K4 is reversed and relay K3 is held at its biased position. With relay K4 reversed then the relays 2P and L3 at the remote station are energized by an obvious circuit including contact I34 of relay K4 and the receiver RI44 is deenergized and transmitter 'IN is energized and conditioned to supply the carrier of 144 kc. The opening of contact I33 of relay K4 removes the shunt circuit from relay DI of unit CTI of station RS and relay DI is picked up so that the receiver R39 is connected to the transverse linev circuit. At the primary station PS, movement of the switch OS to the left closes circuits for energizing relays LI and L2 the same'as. in Fig. 1a and the calling oscillator CO is conditioned to sup-ply the tone frequency for the 144 kc. carrier channel. The output of the oscillator CO is now connected to the input of the transmitter T39 through wire 35 in. cable CAI, contact I48 of switch TS, wire I49. in cable CA2 to a tap at the left-hand end of switch SS, contactISil of switch SS, wire MI in cable CA2, contact I42 of switch TS, wire I43 in'cable. CA4, input of transmitter T39 and terminal BA. This circuit also serves to shunt the relay DI of the unit CTI and transmitter T39 is relay G3 being energized when 18" connected to the transverse'line circuit. Thus the carrier of 39 kc. modulated by the tone frequency of oscillator 00 is transmitted to station RS and there received by receiver R39 of the unit CTI of that station. This calling current is demodulated and the tone frequency is applied to the input of transmitter TN of station RS to modulate the 144 kc. carrier and the corresponding calling current is supplied to the longitudinal line circuit for transmission to the train TR2. The operator restores the switch CS at the end of a calling period and the relay G4 is deenergized and the apparatus made ready to receive a reply from the train. The reply is picked up by the receiver RI44 at station RS and demodulated. The voice frequencies are applied to the transmitterT39 of the remote station and the corresponding carrier telephone current is applied to the transverse line circuit and transmitted to the primary station where it is received and demodulated at receiver R39 of that station. The output of the receiver R39 of station PS is now connected to the earphones through wire 48 in cable CA4, contact I30 of switch TS, wire I3I in cable CA2, contact I3'I of switch SS, wire H in cable CA3 and the earphones to ground.

In replying 'to the train, the operator uses push-to-talk switch 12 which when closed completes the circuit for relay G4, current flowing from terminal B through contact I45 of switch TS, wire I44 in cable CA4, winding of relay G4. wire I41 in cable CA3, contact I6I of switch S5, wire IS in cable CA3 and switch 12 to terminal N. With relay G4 pickedup, control current'of the polarity efiective to reverse the relay K4 at the remote station is transmitted from battery I53 at the primary station, and with relay K4 reversed the relay DI is picked up and the receiver R39 at the remote station is connected to the transverse line circuit. Also the receiver RI44 at station RS is deenergized and transmitter TN is energized and conditioned to supply the 144 kc. carrier.

At the primary station the microphone M is. provided with a circuit includingground, front contact IE6 of relay G4, microphone M, wire I8 in cable CA3, contact I40 of switch SS, wire MI in cable CA2, contact I42 of switch TS, wire I43 in cable CA4, input of transmitter T39,'andterminal BA. This path also serves to shunt the relay DI and relay DI is released so that the output of the transmitter T39 is connected to the transverse line circuit. Ihus carrier telephone current of 39 kc. carrier is transmitted to the remote station RS where it is received and demodulated at receiver R39 and the voice frequency supplied to the transmitter TN with the result that carrier telephone current of the 144 kc. channel is supplied to the longitudinal circuit .for transmission to the train TR2.

It follows from the foregoing description of Figs. 2a and 2b that the operator can carry on a two-way conversation with trains within the range of transmission of the remote station. either carrier channel being used, the operator effecting a pushto-talk control of the remote station by means of a polar line circuit.

It is to be pointed out that at the primary station the loud-speaker remains connected to the receivers not used during a conversation so that an emergency call can be received.

Although I have herein shown and described but two forms of carrier inductive communication system for vehicles embodying my invention, it is understood that various changes and the I 19 modifications may' be made therein within the scope-of the'appended claims without departing from the spirit and scope of my invention. -HaVing thus described myinvention, what I claim is: p 1. In a system for communication between an oflice and a vehicle moving over a stretch of trackway remote from the ofiice, the combination comprising, an ofiice, a stretch of trackway, a wayside station along the stretch, telephone equipment at the station, said equipment including a transmitter having a modulator and a receiver having a demodulator and which equipment uses a carrier of a given frequency for twoway transmission by electromagnetic induction on'a, push-to-talk basis, carrier telephone units one at the office and one at the station, each said unit including a transmitter having a modulator and a receiver having a demodulator and which units use a carrier of a frequency different from said given frequency, a line circuit between said office and station, each said unit having connections to selectively connect the output of its transmitter and the input of its receiver to said line circuit for two-way transmission between the office and station on a push-to-talk basis, said station unit having connections to couple the input of its transmitter and the output of its receiver to the output of the receiver and the input of the transmitter respectively of said station telephone equipment, a telephone set at said ofiice having connections to the input of the transmitter and the output of the receiver of said oflice telephone unit; control means including a push-totalk switch at the ofiice, a line circuit between the oflice and station and control relays one at the ofiice and one at the station; said relays being operated to different positions in response to operation of said push-to-talk switch, said cflice relay having contacts operable to govern said connections of said office unit to the first mentioned line circuit, and said station relay having contacts operable to govern said connections of said'station unit to the first mentioned line circuit and to selectively activate the transmitter and receiver of said station telephone equipment. 2. In a, system for communication between an office and a vehicle moving over a stretch of trackway remote from the omce, the combination comprising, a stretch of traclrway, an office, a station along said stretch, telephone equipment at the station, said equipment including a transmitter having a modulator and a receiver having a demodulator and which equipment uses a carrier of a given frequency for two-way transmission on a push-to-talk basis, carrier telephone units one at the ofiice and one at the station, each said unit including a transmitter having a modulator and a receiver having a demodulator and which units use a carrier of a frequency diiferent from said given frequency for two-way transmission between said ofiice and station on a push-to-talk basis, said station .unit having connections to couple the input of its transmitter and the output of its receiver to the output of the receiver and the input of the transmitter respectively of said station telephone equipment, a telephone set at said office having connections to the input of the transmitter and the output of the receiver of said oflice telephone unit; control means including a push-to-talk switch at the ofiice, a line circuit between the office and station and control relays one at the ofiice and one at the station; said control relays being operated to difierentpositions according to the position of said push-to-talk switch, circuit means including a contact of each of said control relays to alternately couple the output of the transmitter and the input of the receiver of said'ofiice telephoneunit to the input of the'receiver and the output of the transmitter respectively of said station telephone unit in response to operation of the push-to-talk switch, and other circuit means including a contactof said station relay to alternately activate said transmitter and receiver of said station telephone equipment'in response to operation of the pushto-talk switch. 3. In a system for communication between an ofllce and a vehicle moving over a stretch of trackway and which stretch is greater than the efiective range of transmission of the system, the combination comprising, an oflice, a stretch of trackway, a wayside station located along the stretch remote from said oifice; telephone equipments one at said office and one at said station; each said equipment including a transmitter having a modulator and a receiver having a demodulator and which equipments use a given carrier frequency for two-Way transmission by electromagnetic induction on a push-to-talk basis, carrier telephone units one at the ofiice and one at the station, each said unit including a transmitter having a modulator and a receiver having a demodulator and'which units use a carrier frequency different from said given frequency for two-way transmission between the ofiice and'the station on a push-to-talk basis, said station unit having connections to couple the input of its transmitter and the output of its receiver to the output of the receiver and the input of the transmitter respectively of said station telephone equipment, a telephone set at the ofiice, switching means at the otfice operable to a first and a second position, means including contacts of the switching means to connect said telephone set to the office telephone equipment'or to the oflice telephone unit according as the switching means is operated to its first or second position; control means including a push-to-talk button at the ofiice, a line circuit between the office and station and three control relays of which relays'a first and a second one are at the ofiice and a third one is'at the station; said push-to-talk button being operable to control either said first relay or to control said second and third relays according as said switching means is operated to its first or second position, means including a contact governed by said first relay to alternately activate the transmitter and receiver of said ofl ice telephone equipment in response to operation of the push-to-talk button, and means including contacts governed by said second and third relays to alternately couple the transmitter and receiver of the oflice telephone unit to the receiver and transmitter respectively of the station telephone unit and to alternately activate the transmitter and receiver of the station telephone equipment in response to operation of the push-to-talk but- 4. In combination, an omce and a station spaced apart, line wires extending between said ofiice and station, a longitudinal line circuit including said line wires in multiple and aground return path, a transverse line circuit including said line wires in series, a first and a second carrler converting means at said station, said first means including means which are operable for converting a carrier telephone current of a given first carrier frequency into a carrier telephone 21 current of a given second carrier frequency, said second means including means which are operable for converting a carrier telephone current of said second carrier frequency into carrier telephone current of said first carrier frequency, circuit means at said station to connect the input and the output of said first and second converting means respectively to said transverse line circuit, other circuit means at said station to connect the output and the input of said first and second converting means respectively to said longitudinal line circuit, a carrier telephone unit including a receiver having a demodulator and a transmitter having a modulator at said office and which receiver and transmitter use said given first carrier frequency, circuit connections whereby the input of said oifice receiver and the output of said ofiice transmitter are connec ted to said transverse line circuit, a telephone set at said office having connections to the input and the output of said ofiice transmitter and receiver respectively, a push-to-talk device and a source of control current at said office, said control source supplying current differentfrom said first and second carrier and having connections to said line wires, a control relay means at said station connected to said line wires by means whereby the control relay means is responsive only to current of the control source, means includin contacts controlled by said push-to-talk device to govern the supplying of current by said control source and the energizing of said ofiice receiver and transmitter, and means including contacts controlled by said relay means to govern the energizing of said first and second converting means.

5. In combination, a primary and a secondary station, a pair of line wires, a transverse circuit including said line wires in series, a longitudinal circuit including said line wires in multiple and a common return path, a carrier telephone equipment at said secondary station including a transmitter having a modulator and a receiver having a demodulator, said equipment adapted to use a carrier of a given frequency and provided withconnections to couple the input of its receiver and the output of its transmitter to said longitudinal circuit, carrier telephone units one at each said primary and secondary stations, each said unit including a, transmitter having a modulator and a receiver having a demodulator and adapted to use a carrier havin a selected frequency different from said given frequency, a telephone hand set at said primary station having an earphone and a microphone which are connected to the output of the receiver and the input of the transmitter respectively of said telephone unit of the primary station, circuit means to couple the output of the receiver and the input of the transmitter of said telephone unit at the secondary station to the input of the transmitter and the output of the receiver respectively of said telephone equipment, a first anda second control relay, a control current source at said primary station adapted to supply current of a selected frequency different from either of said carrier frequencies and having connections to said transverse circuit, means including a filler adapted to pass said control current to connect said second control relay to said transverse circuit, means including a contact of said first control relay to selectively connect either output of the transmitter or the input of the receiver of said telephone unit at said primary station to said transverse circuit, means including a contact of said second control relay to selectively connect the input of the receiver and the output of the transmitter of said telephone unit at said secondary station to said transverse circuit and to selectively activate either the receiver or the transmitter of said telephone equipment, c, push-to-talk device, and a mitter having a modulator and a receiver having a demodulator, said equipment adapted to use a carrier of a given frequency and provided with connections to couple the input of its receiver and the output of its transmitter to said longitudinal circuit, carrier telephone units one at each said primary and secondary stations, each said unit including a transmitter having a modulator and a receiver having a demodulator and adapted to use a carrier having a, selected frequency different from said given frequency, a telephone hand set at said primary station having an earphone and a microphone which are connected to the output of the receiver and the input of the transmitter respectively of said telephone unit of the primary station, circuit means to couple the output of the receiver and the input of the transmitter of said telephone unit at the secondary station to the input of the transmitter and the output of the receiver respectively of said telephone equipment, a first control relay at the primary station, a polar control relay at said secondary station, a control source of direct current,

repeater coils one at each of said stations, means including a first one of said coils and contacts of said first relay to reversibly connect said direct current source between said line wires in multiple and ground, means including a second one of said coilsto connect said polar relay between said line wires in multiple and ground, means including a contact of said first control relay to selectively connect either the output of the transmitter or the input of the receiver of the telephone unit of the primary station to said transverse circuit;

means including contacts of said polar relay to selectively connect either the input of the receiver or the output of the transmitter of the telephone unit of the secondary station to said transverse circuit andto selectively activate either the receiver or the transmitter of said telephone equipment, a push-to-talk device, and a circuit including said push-to-talk device .to at times energize said first control relay.

' ELBERT W, MARLOWE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,453,387 Espenschied et a1. May 1, 1923 2,393,291 Clark Jan. 22, 1946 2,398,741 Halstead Apr. 16, 1946 

